Historically, re-refining waste oil has been difficult to undertake economically unless conducted on a large scale. While complex large scale processing facilities for recycling waste oils and converting them to reusable products are known, due to the expense of the known technologies, large scale capital intensive process facilities are required to draw on large geographical catchment areas for waste oil feedstock. Due to feedstock, transportation, and logistics costs, which may quickly consume any economies of scale benefit, large scale processing facilities are only viable in large regional markets able to supply sufficient quantities of waste oil feedstocks within a reasonable distance. In smaller and developing markets where such large scale operations are not sustainable, it has not been possible to economically re-refine waste oils with known technology. What is needed is a way to re-refine or reprocess oil cost effectively to accommodate smaller markets both for specific industries and smaller, possibly less developed and/or isolated, population areas.
Presently, there are no economically viable technology solutions for processing waste oil in smaller markets and trading areas where re-refining capacity is insufficient or non-existent. Therefore, current practices in markets too small to support conventional re-refining facilities include burning waste oil as a dirty fuel for industrial use or space heating, or alternatively disposing of large volumes of waste oil in potentially environmentally inappropriate ways. These practices may result in a discharge of air borne pollutants, or contamination of soils and groundwater. Whichever practice is used, the resulting water, soil, and/or air pollution contains many of the harmful chemicals found in waste oil, which may expose plants, animals, and humans to their toxic effects. Therefore, in many jurisdictions around the world, most waste oil is classified as a hazardous waste material. What is needed is a solution to economically recycle these waste oils in a more environmentally friendly manner.
There are a number of existing methods/processes for converting waste oils to diesel or diesel-like fuels. For example, U.S. Pat. Nos. 5,271,808 and 5,286,349 issued to Shurtleff disclose a process and equipment design for converting waste oil to diesel. However, these processes, typical of the refining industry, operate at high pressure and high temperature in their heated reactor vessel. Such conditions during thermal pyrolysis are known to result in unwanted coke fouling making continuous, long term operation a challenge that all petroleum refineries have to continually address at significant operating and maintaining cost.
A number of approaches have been developed to attempt to overcome the coke formation issue and the resultant difficult to control operation. For example, U.S. Pat. No. 5,885,444 issued to Wansbrough et al. discloses a system where the heat for pyrolysis of the waste oil is provided by high volume circulation of the waste oil through an external heat recovery system and reactor system. In addition, a heavy fuel oil containing coke particles and potential coke precursors is continuously removed from the reactor vessel. As another example, U.S. Pat. No. 6,132,596 issued to Yu discloses a system where pyrolysis heat is added via rapid circulation of waste oil from a reactor vessel, through the tubes of a fired heater and back into the reactor under high pressure. As the reaction proceeds, coke and coke precursors build up in the reactor and on the walls of the fired heater tubes, requiring the operator to subject the process to a high temperature treatment to convert all residual material to coke or vapours. The coke then must be physically cleaned from the inside of the reactor and the fired heater tubes.
In a further example of an existing method for converting waste oil, U.S. Pat. No. 7,255,785 discloses the transient operation of pyrolysis system whereby the waste oil is heated to 300-350° C. and then subjected to very high vacuum conditions (i.e. 10−6 torr) to allow additional evaporation and cracking to occur. However, this system is more complicated to operate than traditional continuous flow processes and may result in only about 70% conversion of the feed oil.